While not an exact comparison, Amazon's total sales are estimated to have topped $4.2 billion over the company's 36-hour Prime Day event in July, according to Wedbush Securities Inc. analyst Michael Pachter. Amazon does not release Prime Day sales figures, but the company said it was "the biggest shopping event in Amazon history," exceeding sales from Cyber Monday, Black Friday, and the previous Prime Day.

Over the last decade, Alibaba has almost single-handedly turned Singles Day — November 11, or 11/11 — into a cultural phenomenon and by far the biggest day of the year for online shopping.

The explosive start to Singles Day comes as little surprise despite some recent shakiness in the Chinese economy. A decade of skyrocketing 11/11 sales brings an added pressure to post ever-higher figures, according to Dr. Daniel Zipser, a McKinsey & Company senior partner who leads its consumer and retail practice in Greater China.

"The whole world is looking," when it comes to Singles Day sales figures, Zipser told Business Insider on Saturday.

Alibaba is not a retailer itself, so Singles Day sales figures are equal to gross merchandise volume, or the total value of goods ordered through the company's marketplace, which includes Taobao.com, Tmall, and concepts that blend online and offline sales, like the supermarket chain Hema.